The present invention relates, in general, to an improved gyrotron traveling-wave device and, more particularly, to a novel method for reducing spurious oscillations thereby improving the efficiency of the device.
The gyrotron is a new type of microwave device employing the electron cyclotron maser mechanism. It ideally consists of an ensemble of monoenergetic electrons following helical trajectories around the lines of an axial magnetic field inside a fast wave structure such as a metallic tube or waveguide. The physical mechanism responsible for the radiation in the gyrotron has its origin in a relativistic effect. Initially, the phases of the electrons in their cyclotron orbits are random, but phase bunching (relativistic azimuthal bunching) can occur because of the dependence of the electron cyclotron frequency on the relativistic electron mass. Those electrons which lose energy to the wave become lighter, rotate faster, and, hence, accumulate phase lead, while those electrons which gain energy from the wave become heavier, rotate slower, and accumulate phase lag. This rotating electron interaction with the wave results in phase bunching such that the electrons radiate coherently and amplify the wave.
In essence, there is an intrinsic preference for relativistic azimuthal phase bunching in the presence of an electromagnetic wave. If the incident wave has a frequency slightly larger than the electron cyclotron frequency or its harmonics, then stimulated emission will occur. Since this bunching mechanism occurs in phase with the electromagnetic wave, the stimulated radiation emission from the bunching is also emitted in phase with the wave, leading to wave amplification.
One of the many problems experienced in gyrotron devices is the presence of undesirable parasitic oscillations. These oscillations alter the quality of the electron beam within the device by causing electron bunching at other than the desired frequency of operation. The parasitic oscillations thus interfere with the operation of the device resulting in a large reduction in the device's efficiency.
The present invention presents a novel solution to the parasitic oscillation problem by providing an improved method for absorbing these oscillations. The entire electron beam energy is then applied to the desired frequency, or mode, of operation with little or no deviation due to unwanted oscillations.